Turn off brush overlay in Texture Paint mode?
Im not sure if this will help, but i think its the answer your looking for..

In Texture Paint, on the tools tab on the Left (shown in your picture)
underneath radius and strength, is a blend option.. you have it set to "Mix" you can change this to lighten, Darken, Multiply, Subtract, etc..

try messing around with these options and see if that helps